The invention relates to a pilot-controlled directional valve which is especially suitable for flight control hydraulic systems.
Fluid to such flight control hydraulic systems is provided by pumps and usually there is the possibility to shut off and to admit fluid pressure by a three-way directional valve. The hydraulic system usually is connected to several driven devices such as hydraulic servo drives for aircraft control surfaces and auxiliary functions such as moving a freight door. When the aircraft is to be serviced, the hydraulic system is driven by an electric pump so that aircraft functions can be checked and the freight door can be actuated. Since the service personal may go on the wings of the aircraft during service in the airport, it must be strictly avoided to move control surfaces as long as the aircraft is serviced.